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Fri, 10 Jul 2020 05:39:57 +0000 From: "Liu, Yi L" To: Alex Williamson Subject: RE: [PATCH v3 06/14] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST (alloc/free) Thread-Topic: [PATCH v3 06/14] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST (alloc/free) Thread-Index: AQHWSgRRzB2G/Oy5QEmxCHQWFS0FB6j02KQAgACUCyCAB/5SUIAAxDYAgABLnwCAABmKAIAAAO4wgAAFFYCAAAD78IAASzDwgAB/qYCAAOQrQA== Date: Fri, 10 Jul 2020 05:39:57 +0000 Message-ID: References: <1592988927-48009-1-git-send-email-yi.l.liu@intel.com> <1592988927-48009-7-git-send-email-yi.l.liu@intel.com> <20200702151832.048b44d1@x1.home> <20200708135444.4eac48a4@x1.home> <20200709082751.320742ab@x1.home> In-Reply-To: <20200709082751.320742ab@x1.home> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-reaction: no-action dlp-version: 11.2.0.6 dlp-product: dlpe-windows authentication-results: redhat.com; dkim=none (message not signed) header.d=none;redhat.com; dmarc=none action=none header.from=intel.com; x-originating-ip: [192.198.147.206] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 5e65f010-c4e7-4641-58f5-08d82493ae85 x-ms-traffictypediagnostic: DM6PR11MB4642: x-ld-processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:6790; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" Hi Alex, > From: Alex Williamson > Sent: Thursday, July 9, 2020 10:28 PM > > On Thu, 9 Jul 2020 07:16:31 +0000 > "Liu, Yi L" wrote: > > > Hi Alex, > > > > After more thinking, looks like adding a r-b tree is still not enough to > > solve the potential problem for free a range of PASID in one ioctl. If > > caller gives [0, MAX_UNIT] in the free request, kernel anyhow should > > loop all the PASIDs and search in the r-b tree. Even VFIO can track the > > smallest/largest allocated PASID, and limit the free range to an accurate > > range, it is still no efficient. For example, user has allocated two PASIDs > > ( 1 and 999), and user gives the [0, MAX_UNIT] range in free request. VFIO > > will limit the free range to be [1, 999], but still needs to loop PASID 1 - > > 999, and search in r-b tree. > > That sounds like a poor tree implementation. Look at vfio_find_dma() > for instance, it returns a node within the specified range. If the > tree has two nodes within the specified range we should never need to > call a search function like vfio_find_dma() more than three times. We > call it once, get the first node, remove it. Call it again, get the > other node, remove it. Call a third time, find no matches, we're done. > So such an implementation limits searches to N+1 where N is the number > of nodes within the range. I see. When getting a free range from user. Use the range to find suited PASIDs in the r-b tree. For the example I mentioned, if giving [0, MAX_UNIT], will find two nodes. If giving [0, 100] range, then only one node will be found. But even though, it still take some time if the user holds a bunch of PASIDs and user gives a big free range. > > So I'm wondering can we fall back to prior proposal which only free one > > PASID for a free request. how about your opinion? > > Doesn't it still seem like it would be a useful user interface to have > a mechanism to free all pasids, by calling with exactly [0, MAX_UINT]? > I'm not sure if there's another use case for this given than the user > doesn't have strict control of the pasid values they get. Thanks, I don't have such use case neither. perhaps we may allow it in future by adding flag. but if it's still useful, I may try with your suggestion. :-) Regards, Yi Liu > Alex > > > > From: Liu, Yi L > > > Sent: Thursday, July 9, 2020 10:26 AM > > > > > > Hi Kevin, > > > > > > > From: Tian, Kevin > > > > Sent: Thursday, July 9, 2020 10:18 AM > > > > > > > > > From: Liu, Yi L > > > > > Sent: Thursday, July 9, 2020 10:08 AM > > > > > > > > > > Hi Kevin, > > > > > > > > > > > From: Tian, Kevin > > > > > > Sent: Thursday, July 9, 2020 9:57 AM > > > > > > > > > > > > > From: Liu, Yi L > > > > > > > Sent: Thursday, July 9, 2020 8:32 AM > > > > > > > > > > > > > > Hi Alex, > > > > > > > > > > > > > > > Alex Williamson > > > > > > > > Sent: Thursday, July 9, 2020 3:55 AM > > > > > > > > > > > > > > > > On Wed, 8 Jul 2020 08:16:16 +0000 "Liu, Yi L" > > > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi Alex, > > > > > > > > > > > > > > > > > > > From: Liu, Yi L < yi.l.liu@intel.com> > > > > > > > > > > Sent: Friday, July 3, 2020 2:28 PM > > > > > > > > > > > > > > > > > > > > Hi Alex, > > > > > > > > > > > > > > > > > > > > > From: Alex Williamson > > > > > > > > > > > Sent: Friday, July 3, 2020 5:19 AM > > > > > > > > > > > > > > > > > > > > > > On Wed, 24 Jun 2020 01:55:19 -0700 Liu Yi L > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > This patch allows user space to request PASID > > > > > > > > > > > > allocation/free, > > > > > e.g. > > > > > > > > > > > > when serving the request from the guest. > > > > > > > > > > > > > > > > > > > > > > > > PASIDs that are not freed by userspace are > > > > > > > > > > > > automatically freed > > > > > > > when > > > > > > > > > > > > the IOASID set is destroyed when process exits. > > > > > > > > > [...] > > > > > > > > > > > > +static int vfio_iommu_type1_pasid_request(struct > > > > > > > > > > > > +vfio_iommu > > > > > > > *iommu, > > > > > > > > > > > > + unsigned long arg) { > > > > > > > > > > > > + struct vfio_iommu_type1_pasid_request req; > > > > > > > > > > > > + unsigned long minsz; > > > > > > > > > > > > + > > > > > > > > > > > > + minsz = offsetofend(struct > > > > vfio_iommu_type1_pasid_request, > > > > > > > > range); > > > > > > > > > > > > + > > > > > > > > > > > > + if (copy_from_user(&req, (void __user *)arg, minsz)) > > > > > > > > > > > > + return -EFAULT; > > > > > > > > > > > > + > > > > > > > > > > > > + if (req.argsz < minsz || (req.flags & > > > > > > > > ~VFIO_PASID_REQUEST_MASK)) > > > > > > > > > > > > + return -EINVAL; > > > > > > > > > > > > + > > > > > > > > > > > > + if (req.range.min > req.range.max) > > > > > > > > > > > > > > > > > > > > > > Is it exploitable that a user can spin the kernel for a > > > > > > > > > > > long time in the case of a free by calling this with [0, > > > > > > > > > > > MAX_UINT] regardless of their > > > > > > > > actual > > > > > > > > > > allocations? > > > > > > > > > > > > > > > > > > > > IOASID can ensure that user can only free the PASIDs > > > > > > > > > > allocated to the > > > > > > > user. > > > > > > > > but > > > > > > > > > > it's true, kernel needs to loop all the PASIDs within the > > > > > > > > > > range provided by user. > > > > > > > > it > > > > > > > > > > may take a long time. is there anything we can do? one > > > > > > > > > > thing may limit > > > > > > > the > > > > > > > > range > > > > > > > > > > provided by user? > > > > > > > > > > > > > > > > > > thought about it more, we have per-VM pasid quota (say > > > > > > > > > 1000), so even if user passed down [0, MAX_UNIT], kernel > > > > > > > > > will only loop the > > > > > > > > > 1000 pasids at most. do you think we still need to do something on > it? > > > > > > > > > > > > > > > > How do you figure that? vfio_iommu_type1_pasid_request() > > > > > > > > accepts the user's min/max so long as (max > min) and passes > > > > > > > > that to vfio_iommu_type1_pasid_free(), then to > > > > > > > > vfio_pasid_free_range() which loops as: > > > > > > > > > > > > > > > > ioasid_t pasid = min; > > > > > > > > for (; pasid <= max; pasid++) > > > > > > > > ioasid_free(pasid); > > > > > > > > > > > > > > > > A user might only be able to allocate 1000 pasids, but > > > > > > > > apparently they can ask to free all they want. > > > > > > > > > > > > > > > > It's also not obvious to me that calling ioasid_free() is only > > > > > > > > allowing the user to free their own passid. Does it? It > > > > > > > > would be a pretty > > > > > > > > > > > > Agree. I thought ioasid_free should at least carry a token since > > > > > > the user > > > > > space is > > > > > > only allowed to manage PASIDs in its own set... > > > > > > > > > > > > > > gaping hole if a user could free arbitrary pasids. A r-b tree > > > > > > > > of passids might help both for security and to bound spinning in a > loop. > > > > > > > > > > > > > > oh, yes. BTW. instead of r-b tree in VFIO, maybe we can add an > > > > > > > ioasid_set parameter for ioasid_free(), thus to prevent the user > > > > > > > from freeing PASIDs that doesn't belong to it. I remember Jacob > > > > > > > mentioned it > > > > > before. > > > > > > > > > > > > > > > > > > > check current ioasid_free: > > > > > > > > > > > > spin_lock(&ioasid_allocator_lock); > > > > > > ioasid_data = xa_load(&active_allocator->xa, ioasid); > > > > > > if (!ioasid_data) { > > > > > > pr_err("Trying to free unknown IOASID %u\n", ioasid); > > > > > > goto exit_unlock; > > > > > > } > > > > > > > > > > > > Allow an user to trigger above lock paths with MAX_UINT times > > > > > > might still > > > > > be bad. > > > > > > > > > > yeah, how about the below two options: > > > > > > > > > > - comparing the max - min with the quota before calling ioasid_free(). > > > > > If max - min > current quota of the user, then should fail it. If > > > > > max - min < quota, then call ioasid_free() one by one. still trigger > > > > > the above lock path with quota times. > > > > > > > > This is definitely wrong. [min, max] is about the range of the PASID > > > > value, while quota is about the number of allocated PASIDs. It's a bit > > > > weird to mix two together. > > > > > > got it. > > > > > > > btw what is the main purpose of allowing batch PASID free requests? > > > > Can we just simplify to allow one PASID in each free just like how is > > > > it done in allocation path? > > > > > > it's an intention to reuse the [min, max] range as allocation path. currently, > we > > > don't have such request as far as I can see. > > > > > > > > > > > > > - pass the max and min to ioasid_free(), let ioasid_free() decide. should > > > > > be able to avoid trigger the lock multiple times, and ioasid has have a > > > > > track on how may PASIDs have been allocated, if max - min is larger than > > > > > the allocated number, should fail anyway. > > > > > > > > What about Alex's r-b tree suggestion? Is there any downside in you mind? > > > > > > no downside, I was just wanting to reuse the tracks in ioasid_set. I can add a > r-b > > > for allocated PASIDs and find the PASIDs in the r-b tree only do free for the > > > PASIDs found in r-b tree, others in the range would be ignored. > > > does it look good? > > > > > > Regards, > > > Yi Liu > > > > > > > Thanks, > > > > Kevin > > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu